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Cherry blossom season, Emperor’s sake and Citizen Science

Posted March 25, 2015

The Cherry Blossom Festival is probably the oldest celebrated spring tradition, which has now spread from Japan to multiple spots throughout the world.

Kawazu Sakura blossoms of present day. Credit: Jun Ohashi via Flickr (CC BY-NC-SA 2.0)

Kawazu Sakura blossoms of present day. Credit: Jun Ohashi via Flickr (CC BY-NC-SA 2.0)

Far from being just a delightful messenger of warmer months to come, the date when cherries blossom moves every year and thus is a useful indicator of climate conditions. In fact, records of Kyoto Cherry Blossom Festival go back as far as the 8th century, and have been successfully used to track climate change through the ages.


This particular line was inscribed by Tokistune Hiramatsu in an old court diary dating April 14, 1644*. Little did he know, he would become an example of historic (and, truth be told, accidental) citizen scientist many years later.

While he would have never guessed it himself, Tokistune and many other chroniclers and story-tellers, including monks, and merchants, politicians and emperors themselves, have become lay collectors and reporters of data that is invaluable to science today.

For example, research lead by Yasuyuki Aono at Graduate School of Life and Environmental Sciences, Osaka Prefecture University, has used flowering dates of Prunus jamasakura (Yamazakura cherries native in Japan) to reproduce March mean temperatures from the 9th century onwards. This fills in hundreds of years of knowledge gaps, since direct temperature measurements started only 150 years ago or so.

Cherry Blossom Road into Old Akasaka, Old Tokyo, Japan, ca. 1890s. Credit: Okinawa Soba via Flickr (CC BY-NC-SA 2.0)

Cherry Blossom Road into Old Akasaka, Old Tokyo, Japan, ca. 1890s. Credit: Okinawa Soba via Flickr (CC BY-NC-SA 2.0)

Cherry flowering dates, calibrated according to recent temperature data (modern meteorological observation started at Kyoto in 1881), helped to uncover a number of historic temperature peaks and declines. For example, as researchers indicated in one of their publications in 2010, “The reconstructed tenth century March mean temperatures were around 7°C, indicating warmer conditions than at present. Temperatures then fell until the 1180s, recovered gradually until the 1310s, and then declined again in the mid-fourteenth century.”

Curiously, a peak at the beginning of the fourteenth century in Asia actually corresponds to Medieval Warm Period in Europe. A period that followed – The Little Ice Age – is also evident from three cold spots in flowering data, when reconstructed springtime temperatures were 3°C lower than the present day. These dips were also synchronous with three solar minima, the Spoerer, Maunder and Dalton.

The nature of this research is not unlike numerous science projects today, where “lay people” share their local knowledge, track changes in their environment (including temperature variations through seasons) and otherwise help out scientists with data that would otherwise be out-of-reach.

The main difference of course is that modern citizen scientists are (usually) aware of their contribution to science AND have smartphones and fancy software to do most of the dirty work! Nevertheless, public participation in science is more important now than ever.

For example citizen science projects concerned with historical climate data see here and here. Many more to do with climate change are out there too!

Sources: Primack and Higuchi (2007), Aono and Kazui (2008), Aono and Saito (2010).

* A copy of the diary is stored in Kyoto University Library and can be accessed via this link.

Written by Eglė Marija Ramanauskaitė

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